#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
WAL机制演示程序
"""

import os
import sys

# 添加当前目录到Python路径
current_dir = os.path.dirname(os.path.abspath(__file__))
if current_dir not in sys.path:
    sys.path.insert(0, current_dir)

def main():
    """WAL演示主程序"""
    print("🌟 WAL (Write-Ahead Logging) 机制演示")
    print("=" * 60)
    
    print(f"\n📁 WAL实现文件:")
    print(f"   📄 wal_types.py      - WAL数据类型和结构定义")
    print(f"   📄 wal_manager.py    - WAL管理器核心实现")
    print(f"   📄 wal_reader.py     - WAL文件查看工具")
    print(f"   📄 test_wal.py       - WAL功能测试套件")
    
    print(f"\n🔧 已修改的文件:")
    print(f"   📄 storage_engine.py - 集成WAL到存储引擎")
    print(f"   📄 database_server.py - 事务边界WAL记录")
    
    print(f"\n🚀 使用说明:")
    print(f"   1. 运行测试: python test_wal.py")
    print(f"   2. 查看WAL: python wal_reader.py database/demo_db --summary")
    print(f"   3. 详细记录: python wal_reader.py database/demo_db --detail wal_000001.log")
    print(f"   4. 事务分析: python wal_reader.py database/demo_db --analyze")
    
    print(f"\n💾 WAL文件目录结构:")
    print(f"   database/")
    print(f"   ├── demo_db/")
    print(f"   │   ├── database.meta")
    print(f"   │   ├── demo_db.db")
    print(f"   │   └── wal/                    # WAL目录")
    print(f"   │       ├── wal_000001.log     # WAL日志文件")
    print(f"   │       ├── wal_000002.log     # ...")
    print(f"   │       ├── wal.control        # WAL控制文件")
    print(f"   │       └── wal.checkpoint     # 检查点文件")
    print(f"   └── ...")
    
    print(f"\n🎯 WAL机制特性:")
    print(f"   ✅ 事务日志记录 (BEGIN/COMMIT/ROLLBACK)")
    print(f"   ✅ 数据变更追踪 (INSERT/UPDATE/DELETE)")
    print(f"   ✅ 页面级WAL记录")
    print(f"   ✅ 并发事务支持")
    print(f"   ✅ 检查点机制")
    print(f"   ✅ 后台页面刷新")
    print(f"   ✅ WAL文件轮转")
    print(f"   ✅ 崩溃恢复基础设施")
    
    print(f"\n🔍 WAL记录格式:")
    print(f"   📋 事务开始: [LSN] BEGIN transaction_id")
    print(f"   📋 数据插入: [LSN] INSERT table_name {{after_image}}")
    print(f"   📋 数据更新: [LSN] UPDATE table_name {{before}} -> {{after}}")
    print(f"   📋 数据删除: [LSN] DELETE table_name {{before_image}}")
    print(f"   📋 事务提交: [LSN] COMMIT transaction_id")
    print(f"   📋 检查点:   [LSN] CHECKPOINT {{flushed_pages}}")
    
    print(f"\n⚡ 性能优化:")
    print(f"   🚀 WAL缓冲区批量写入")
    print(f"   🚀 后台异步页面刷新")
    print(f"   🚀 定期检查点减少恢复时间")
    print(f"   🚀 WAL文件大小限制和轮转")
    
    print(f"\n🛡️ 可靠性保障:")
    print(f"   🔒 WAL先于数据写入磁盘 (WAL规则)")
    print(f"   🔒 事务提交前强制刷新WAL")
    print(f"   🔒 校验和验证数据完整性")
    print(f"   🔒 支持系统崩溃后恢复")
    
    print("\n" + "=" * 60)
    print("🎉 WAL机制实现完成！")
    print("💡 您的数据库系统现在具备了企业级的数据可靠性保障。")


if __name__ == "__main__":
    main()
